12.7-mm M55 quad anti-aircraft gun

The 12.7-mm M55 anti-aircraft gun consists of the M45C mount and the M20 two-wheel trailer. The power-driven, semi-armored mount has two side-mounted 12.7-mm M2 heavy-barrel (HB) machine guns. The gunner has two control handles. Firing and loading is automatic as long as the operator depresses the triggers of the handles.

The gunner aims the weapons using an M18 reflex sight, which projects a graticule image, focused at infinity, on an inclined glass plate. The graticule image...